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Abstract
The goal of this lesson is for students to develop of an
understanding of how water and blood react in a spattering
situation. Students will perform simple tests to show the properties
of surface tension, viscosity, and calculate specific gravity.
Students will use Internet resources to determine what similarities
exist between simulated human blood and water with respect to
viscosity, surface tension, specific gravity, and size of droplets.
They will illustrate the comparisons between the two substances.
This comparison sets the stage for the upcoming lessons.
Lesson fundamental understandings:
Essential
Questions: The essential question is: How are water
droplets and blood droplets the same?
By the end of this lesson,
students should understand that water droplets are a good model for
blood droplets because their characteristics are so similar.
Standards
National Standards NSES CONTENT
STANDARD: Unifying Concepts and Processes TECHNOLOGY STANDARDS:
Students use technology tools to process data and report results.
INFORMATION LITERACY STANDARDS: Standard 1: The student who is
information literate accesses information efficiently and
effectively. Standard 2: The student who is information literate
evaluates information critically and competently. Standard 3: The
student who is information literate uses information accurately and
creatively.
State Standards Georgia: Process Skills
Nevada: Process Skills #19
Lesson
Prerequisite Skills
Students should be familiar with Internet research techniques as
well as basic ideas about experimental design, safety, and general
lab procedures. Students should be familiar will using a graphic
organizer such as a Venn diagram to illustrate comparisons between
items.
Teacher
Information/Situations/Setting/Time Time Frame: 100
minutes
Situation: Students should work in small groups of two or
three.
Materials/Resources:
needles (or thin wire or 4
staples) (1 per group)
water
theatrical blood (corn syrup,
corn starch, red food coloring, green food coloring)
honey
(enough to fill one test tube per group)
mineral oil (enough to
fill one test tube per group)
test tubes (4 per group)
glass
beads (4 per group)
stoppers to fit test tubes (4 per
group)
pennies (4 per group)
droppers (4 per
group)
graduated cylinder (4 per group)
balance (at least one
for the class, more if available)
evaporating dish for each
group
stopwatch for each group
test tube rack for each
group
droppers (4 for each group)
forceps (1 for each
group)
dishwashing liquid
Pre-lesson preparation
1.
Prepare theatrical blood as follows:
160 mL corn syrup
80 mL
water
44 g corn starch
15 mLs-25 mLs red food coloring
2-3
drops green food coloring
Mix the corn starch thoroughly with the
water. Add the corn syrup. Mix well. Add red food coloring to the
mixture using only 3 teaspoons at first. Then add a couple of drops
of green food coloring to take the "pink" edge off the red coloring.
If the mixture is too light, add one or two teaspoons more of red
food coloring. Add an extra drop of green food coloring if the
mixture gets too pink again. (Real blood is slightly on the dark red
to reddish brown side when it is not fresh from the heart.)
2.
Prepare some test tubes for viscosity measurements as follows. For
each group of students, prepare four tubes - one of water, one of
theatrical blood, one of mineral oil, and one of honey. You may
substitute other materials for the honey and mineral oil, such as
different grades of motor oil. All test tubes must be the same size.
Add glass bead to each tube, fill with the liquids, and then tightly
stopper. There should be NO bubbles in the test tubes. AS YOU ARE
PREPARING THE TUBES, mark each tube with the exact volume of liquid
it contains, and the combined mass of the empty test tube, stopper,
and glass bead.
3. Have a copy of the activity available for
each student.
Teacher Key to Questions:
1. surface
tension
2. Answers will vary depending on substances used.
Hopefully water and blood will yield similar responses.
3. so as
not to destroy the surface tension
4. surface tension
5.
Answers will vary depending on substances used. Hopefully water and
blood will yield similar responses.
6. viscosity
7. Answers
will vary depending on substances used. Hopefully water and blood
will yield similar responses.
8. density; g/mL
9. Answers will
vary depending on substances used. Hopefully water and blood will
yield similar responses.
10. specific gravity; no units
11.
Answers will vary depending on substances used. Hopefully water and
blood will yield similar responses.
Density trend and specific
gravity trend should be the same.
12. Ideally students should
realize that blood and water have similar enough properties so that
water may be used as a substitute when studying spatter
patterns.
Assessment
As a formative assessment, the teacher can check for
understanding by reviewing student responses to the comparison
between water and blood and the student responses to the concepts of
surface tension, viscosity, and specific gravity. The answer key for
these questions is found in the teacher section.
Student Activity/Tasks Working in groups
of two or three, students will do a hands-on investigation in Part A
to observe the properties of surface tension, viscosity, and
specific gravity. In Part B, students will use the Internet to find
the explanations of surface tension, viscosity, and specific gravity
and the published similarities between water and blood with respect
to these properties. They will answer questions about the hands-on
activity as well as the published Internet
information.
Student Activity:
Part A: Hands-On
Investigation Into Properties
1. Gather the following materials
for your group:
a needle or piece of thin wire or four
staples
clean evaporating dish
a penny
4 stoppered test
tubes - each with a different liquid
10-15 mL samples of the four
liquids
graduated cylinder
stopwatch
test tube
rack
dropper (4 for each group)
forceps
dishwashing
liquid
2. Have a sheet of paper and pen available to record
data.
3. Using a clean evaporating dish with no soap residues,
try to float a needle, a thin piece of wire, or a staple on one of
the liquids. Your hands need to be clean and free of lotions and
soaps. Record data. If the object floats, place one drop of
dishwashing liquid in the dish and observe what happens. Record.
4. Put a clean penny on the tabletop. Dropwise, add one of the
liquids to the penny, counting how many drops will fit on the
surface of the penny before overflowing. Be sure to have the penny
with the same side up each time. Perform three trials for each
liquid, cleaning the penny before changing to another liquid.
5.
Using the four stoppered test tubes and a stopwatch, turn the test
tube upside down. Time how long the glass bead takes to travel to
the bottom of the test tube (or really, to the top of the test
tube). Repeat for at least three trials each and record data. DO NOT
OPEN THE TEST TUBES!
6. Using the test tubes of the four liquids,
determine the mass of each full test tube. DO NOT OPEN THE TEST
TUBES! Record the mass of the empty tube (recorded on the tube), the
volume (recorded on the tube), and the mass of the full tube (from
your measurement).
7. For each liquid used, subtract the mass of
the empty tube from the mass of the full tube. This gives the mass
of the liquid. Divide the mass of the liquid by the volume of the
liquid. Record calculations with correct units.
8. For the blood
and the two oils, divide the answer from Step #7 by the answer from
Step #7 for water. Record calculations with units.
Part B:
Internet Investigation of Properties
1. Using the following
Internet sites, research the characteristics that water and blood
have in common. Concentrate on the properties of surface tension,
viscosity, and specific gravity since these play a large role in the
blood spatter patterns that you will be investigating in subsequent
lessons. Do not limit yourself to these properties since other
information will be invaluable to you as you proceed forward in this
unit.
www.chemistry-info.net/
www.branta.connectfree.co.uk/surface_tension.htm
http://edie.cprost.sfu.ca/~rhlogan/viscous.html
2.
Schematically show the similarities and differences between water
and blood. For example, use a Venn diagram, a concept map, or a
program like Inspiration to show your results.
Answer the
following questions:
1. From Part A, what property is being
investigated in Step #3?
2. Describe how the results for the
liquids varied or were the same from Step #3.
3. Why is it
important to have your hands free of soaps and lotions in Step
#3?
4. From Part A, what property is being investigated in Step
#4?
5. Describe how the results for the liquids varied or were
the same from Step #4.
6. From Part A, what property is being
investigated in Step #5?
7. Describe how the results for the
liquids varied or were the same from Step #5.
8. From Part A,
what property was being determined in Step #7? What are the correct
units for this property?
9. Describe how the results for the
liquids varied or were the same from Step #7.
10. From Part A,
what property was being determined in Step #8? What are the correct
units for this property?
11. Describe how the results for the
liquids varied or were the same from Step #8. Why is the answer to
this question the same as the answer to Question #9?
12. From
the Internet information and your own investigation, do you think
that the properties of water and simulated blood are similar enough
to substitute water properties for blood properties when studying
spatter patterns? Justify your answer. Hint: Spatter patterns of
liquids depend on viscosity, surface tension, and specific
gravity.
Enrichment/Alternate Activity:
Enrichment: Research blood typing and determine whether the type
of blood, the gender of the person, the ethnic origin of the person,
or the alcohol consumption affects the viscosity, surface tension,
and specific gravity of the blood. Students could do research
individually or in groups and create brochures or make presentations
to the class using Powerpoint, Hyperstudio or any other presentation
software. Research how these properties affect certain products. For
example, what effect does the viscosity of motor oil have on the
performance of the car engine? Why are there different viscosities
available? Are the same viscosities available in all geographic
regions? Why?
Cross-Curricular:
Mathematics is used in collecting data.
Technology
Requirements/Tools/Materials
Students will need a computer with Internet connection for Part B
of this activity. Any software with draw/paint capabilities can be
used to create a Venn diagram to show the comparison between blood
and water. For enrichment activities, Powerpoint or Hyperstudio,
other presentation software, or publishing software would be
helpful, but not mandatory.
Students need to be able to
access the Internet.
Acknowledgements:
Journals with helpful information: Forensic Science Review
Laboratory of Forensic Science The Canadian Society of Forensic
Science Journal Legal Medicine Annual Journal of Forensic Science
Text with helpful information: Bloodstain Patterns by Herbert Leon
MacDonell
Additional Resources
Main
URL:
Related Lessons
Related Resources
Copyright © 1997-2003
Career Connection to Teaching with Technology
USDOE Technology Innovation Challenge Grant
Marshall Ransom, Project Manager
All rights reserved.
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